TECHNICAL FIELD
[0001] The present invention relates to a packing material for a lithium cell and a production
method thereof.
Priority is claimed on Japanese Patent Application No.
2007-249763, filed September 26, 2007, the content of which is incorporated herein by reference.
BACKGROUND ART
[0002] In recent years, lithium cells, which can be made in ultra thin forms and readily
reduced in size, are being actively developed as the cells for use within portable
terminals such as laptop computers and mobile phones, video cameras, and satellites
and the like. In terms of the packing material used within these types of lithium
cells, rather than the metal cases used as the packing material for conventional cells,
multilayer films (such as a configuration including a heat-resistant base material
layer / an aluminum foil layer / and a thermal adhesive film layer) formed in the
shape of a pouch are now frequently being used, as they are lightweight and allow
the shape of the cell to be selected freely.
[0003] Lithium cells contain, as cell contents, a positive electrode material, a negative
electrode material, and either an electrolyte solution prepared by dissolving an electrolyte
(a lithium salt) in an aprotic solvent having a penetrative ability such as propylene
carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate or ethyl methyl
carbonate, or an electrolyte layer formed from a polymer gel impregnated with the
above electrolyte solution. However, if the solvent having a penetrative ability penetrates
through the thermal adhesive film layer that acts as a sealant, then the strength
of the lamination between the aluminum foil layer and the thermal adhesive film layer
tends to deteriorate, and eventually leads to leakage of the electrolyte solution.
Furthermore, as the lithium salt that acts as the electrolyte, LiPF
6 or LiBF
4 or the like is used. Because these salts generate hydrofluoric acid via a hydrolysis
reaction with moisture, they can cause corrosion of metal surfaces or deterioration
in the lamination strength between the various layers of a multilayer film. By using
an aluminum foil, the penetration of moisture from the surface of the packing material
can be substantially blocked. However, in the lithium cell packing material, the multilayer
film typically has a construction that is bonded together by heat sealing, meaning
that hydrolysis of the lithium salt caused by moisture that penetrates via the edge
face of the seal provided by the thermal adhesive film layer that functions as the
sealant remains a concern. Accordingly, strengthening the interlayer adhesive strength
between the aluminum foil and the thermal adhesive film layer in order to improve
the durability (the electrolyte solution resistance and hydrofluoric acid resistance)
of the cell contents is necessary.
Moreover, lithium cells are widely used in portable mobile phones, and the usage environment
may sometimes reach very high temperatures of 60 to 70°C, for example, inside a vehicle
in the middle of summer. A packing material for a lithium cell that exhibits favorable
resistance to the electrolyte solution even under these types of high-temperature
conditions has been keenly sought.
[0004] As a result, various methods are being investigated to inhibit the delamination that
occurs between the aluminum foil layer and the thermal adhesive film layer due to
the effects of the electrolyte solution or the hydrofluoric acid generated by hydrolysis
of the lithium salt that functions as the electrolyte (see Patent Documents 1 to 4).
Patent Documents 1 to 3 disclose packing materials for lithium cells prepared by techniques
such as extrusion lamination or thermal lamination, which do not undergo delamination
even under the effects of the electrolyte solution or hydrofluoric acid. Patent Document
4 discloses a technique of improving the urethane-based adhesive used in a dry lamination
method. This technique yields a urethane-based adhesive with superior electrolyte
solution resistance, meaning a packing material that inhibits delamination can be
obtained even using a dry lamination method.
[0005] However, in recent years, the functions demanded of the lithium cell packing materials
used for packaging lithium cells have continued to increase. One example of a function
now required of the packing material for a lithium cell is water resistance. However,
as described above, because hydrofluoric acid is generated by hydrolysis of the lithium
salt that functions as the electrolyte, evaluations that use water have generally
not been included within the methods used for evaluating the lithium cell packing
material. However, amongst the various environments in which the lithium cell may
be used, accidents such as a situation where a mobile telephone is accidentally dropped
into water can be readily conceived. In such cases, there is a possibility that the
lack of water resistance may cause delamination, or that the increase in hydrofluoric
acid production caused by the excessive absorption of moisture may cause corrosion
of the aluminum foil, resulting in delamination. Accordingly, further improvements
in both the water resistance and hydrofluoric acid resistance are desirable.
For these types of reasons, the necessity of evaluating water resistance as one of
the methods used for evaluating lithium cell packing materials is gradually becoming
more accepted. Typically, when performing an electrolyte solution evaluation for the
lithium cell packing material, a packing material sample cut into a strip is dipped
in the electrolyte solution at a temperature of 85°C. In order to minimize handling
and also include an evaluation of water resistance, a method has been proposed in
which the strip sample is washed with water following the electrolyte solution dipping
treatment, and subsequently subjected to a water dipping treatment. Moreover, an accelerated
test is also sometimes used, in which the dipping treatment at 85°C is conducted using
an electrolyte solution to which several thousand ppm of water has already been added,
thereby performing the evaluation under conditions in which hydrofluoric acid already
exists.
[0006] However, with the lithium cell packing materials disclosed in Patent Documents 1
to 3, the water resistance is not entirely satisfactory. Further, the packing material
disclosed in Patent Document 4 also suffers from poor water resistance.
Furthermore, it is thought that lithium cells will not only be useful in miniaturized
applications such as the types of portable mobile phones and the like mentioned above,
but will also become increasingly important in large-scale applications such as cells
for motor vehicles or the like. Motor vehicle applications, in particular, will require
improvements in the electrolyte solution resistance, water resistance and hydrofluoric
acid resistance beyond current levels.
[0007] The most effective known method of imparting these resistance properties is performing
a chemical conversion treatment on the aluminum foil, and one example of this type
of chemical conversion treatment is a chromate treatment.
For example, Patent Document 5 discloses a multitude of chromate treatments, including
coating type chromate treatments and chromate treatments that employ dipping methods.
Further, in all manner of chemical conversion treatments not limited to chromate treatments,
the aluminum foil may be imparted with an etching function so that the aluminum foil
and the chemical conversion treatment layer formed by the chemical conversion treatment
adopt a graded structure. In order to achieve this effect, any of the various inorganic
acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid and hydrofluoric
acid, or salts thereof, may be used as treatment agents.
[0008] However, in the type of chromate treatment disclosed in Patent Document 5, the hexavalent
chromium used as the main component of the treatment material has been identified
as an environmental toxin, and although it exhibits favorable functionality, the material
is unattractive from an environmental perspective. As a result, trivalent chromium
has become widely used, but achieving the same effect as that observed for hexavalent
chromium is difficult, and as long as chromium continues to be used, chromate treatments
will remain undesirable from an environmental point of view.
Furthermore, the treatment agents used during chemical conversion treatments often
cause corrosion of the coating apparatus, which not only places limitations on the
coating apparatus, but also tends to result in deterioration in the operating environment.
Moreover, in order to improve the adhesion of these treatment agents, a dipping treatment
in an acid bath or alkali bath, and steps for performing degreasing or etching may
be included within the production steps for the cell packing material. However, although
these steps are necessary in term of imparting favorable electrolyte solution resistance,
the treatment cost is high, and the steps tend to be rate-limiting in terms of the
production of the cell packing material, meaning a significant simplification of the
production steps is currently required.
[Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. 2001-243928
[Patent Document 2]
Japanese Unexamined Patent Application, First Publication No. 2004-42477
[Patent Document 3]
Japanese Unexamined Patent Application, First Publication No. 2004-142302
[Patent Document 4]
Japanese Unexamined Patent Application, First Publication No. 2002-187233
[Patent Document 5]
Japanese Unexamined Patent Application, First Publication No. 2002-144479
DISCLOSURE OF INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0009] The present invention takes the above circumstances into consideration, with an object
of providing a packing material for a lithium cell that has no impact from an environmental
perspective, enables a simplification of the production steps, and exhibits excellent
electrolyte solution resistance, hydrofluoric acid resistance and water resistance,
as well as providing a production method for the packing material.
MEANS TO SOLVE THE PROBLEMS
[0010] A packing material for a lithium cell according to the present invention includes
a first adhesive layer, an aluminum foil layer, a coating layer, an adhesive resin
layer or a second adhesive layer, and a sealant layer laminated sequentially on one
surface of a base material layer, wherein the coating layer is a multilayer structure
including a layer (A), in which 1 to 100 parts by mass of a phosphoric acid or a phosphate
has been blended into 100 parts by mass of a rare earth element-based oxide, and a
layer (X) containing an anionic polymer and a cross-linking agent that causes cross-linking
of the anionic polymers.
In the present invention, a relationship between a mass (a) per unit surface area
(g/m
2) of the layer (A), and a mass (x) per unit surface area (g/m
2) of the layer (X) preferably satisfies an expression 2 ≥ x/a.
[0011] Further, the layer (A) is preferably laminated directly onto the aluminum foil layer.
Furthermore, a mass (a) per unit surface area (g/m
2) of the layer (A) is preferably within a range from 0.010 to 0.200 g/m
2.
[0012] Moreover, the coating layer is preferably the multilayer structure further comprising
a layer (Y) containing a cationic polymer and a cross-linking agent that causes cross-linking
of the cationic polymers.
Furthermore, a relationship among a mass (a) per unit surface area (g/m
2) of the layer (A), a mass (x) per unit surface area (g/m
2) of the layer (X), and a mass (y) per unit surface area (g/m
2) of the layer (Y) preferably satisfies an expression 2 ≥ (x+y)/a.
[0013] A packing material for a lithium cell according to the present invention includes
a first adhesive layer, an aluminum foil layer, a coating layer, an adhesive resin
layer or a second adhesive layer, and a sealant layer laminated sequentially on one
surface of a base material layer, wherein the coating layer comprises a layer (M)
containing a rare earth element-based oxide, a phosphoric acid or a phosphate, an
anionic polymer, and a cross-linking agent that causes cross-linking of the anionic
polymers, in which 1 to 100 parts by mass of the phosphoric acid or the phosphate
has been blended into 100 parts by mass of the rare earth element-based oxide.
In the present invention, the coating layer is preferably the multilayer structure
further comprising a layer (Y) containing a cationic polymer and a cross-linking agent
that causes cross-linking of the cationic polymers.
[0014] Further, the cationic polymer is preferably at least one polymer selected from the
group consisting of polyethyleneimines, ionic polymer complexes made of a polyethyleneimine
and a polymer having carboxylic acid groups, primary amine-grafted acrylic resins
having a primary amine grafted to a main acrylic backbone, polyallylamines and derivatives
thereof, and aminophenols.
[0015] Furthermore, the anionic polymer is preferably a copolymer comprising, as a main
component, poly(meth)acrylic acid or a salt thereof, or (meth)acrylic acid or a salt
thereof.
Moreover, the cross-linking agent is preferably at least one material selected from
the group consisting of compounds having an isocyanate group, a glycidyl group, a
carboxyl group or an oxazoline group as a functional group, and silane coupling agents.
[0016] Furthermore, the rare earth element-based oxide is preferably cerium oxide.
Moreover, the phosphoric acid or phosphate is preferably a condensed phosphoric acid
or a condensed phosphate.
[0017] Furthermore, the adhesive resin layer is preferably composed of (i) or (ii) below,
and the second adhesive layer is composed of (iii) below.
- (i) an acid-modified polyolefin-based resin (α).
- (ii) a resin composition in which an acid-modified polyolefin-based resin (α) (30
to 99% by mass) is combined with an isocyanate compound or derivative thereof (β)
and a silane coupling agent (γ) ((β) + (γ): 1 to 70% by mass), provided that if (β)
+ (γ) is deemed to be 100, then (β) : (γ) = 10 to 90 mass : 90 to 10.
- (iii) a polyurethane-based adhesive comprising a polyol component as a main component,
and an isocyanate compound or derivative thereof as a curing agent.
[0018] A production method for a packing material for a lithium cell according to the present
invention includes sequentially laminating a first adhesive layer, an aluminum foil
layer, a coating layer, an adhesive resin layer or a second adhesive layer, and a
sealant layer on one surface of a base material layer, wherein the coating layer is
laminated on top of the aluminum foil layer by applying a coating composition (A),
which comprises a rare earth element-based oxide and 1 to 100 parts by mass of a phosphoric
acid or a phosphate per 100 parts by mass of the rare earth element-based oxide, onto
the aluminum foil layer and subsequently drying the coating composition (A) to form
a layer (A); and applying a coating composition (X), which comprises an anionic polymer
and a cross-linking agent that causes cross-linking of the anionic polymers, onto
the layer (A) and subsequently drying the coating composition (X) to form a layer
(X).
[0019] In the present invention, the coating layer is preferably laminated on top of the
aluminum foil layer by further applying a coating composition (Y), which comprises
a cationic polymer and a cross-linking agent that causes cross-linking of the cationic
polymers, onto the layer (A) or the layer (X), and subsequently drying the coating
composition (Y) to form a layer (Y).
[0020] The production method for a packing material for a lithium cell according to the
present invention includes sequentially laminating a first adhesive layer, an aluminum
foil layer, a coating layer, an adhesive resin layer or a second adhesive layer, and
a sealant layer on one surface of a base material layer, wherein the coating layer
is laminated on top of the aluminum foil layer by applying a coating composition (M),
which comprises a rare earth element-based oxide, 1 to 100 parts by mass of a phosphoric
acid or a phosphate per 100 parts by mass of the rare earth element-based oxide, an
anionic polymer, and a cross-linking agent that causes cross-linking of the anionic
polymers, onto the aluminum foil layer and subsequently drying the coating composition
(M) to form a layer (M).
[0021] In the present invention, the coating composition (M) preferably has a relationship
that satisfies an expression 2 ≥ x'/a' between a total mass (a') (g) of the rare earth
element-based oxide, and the phosphoric acid or the phosphate, and a total mass (x')
(g) of the anionic polymer and the cross-linking agent that causes cross-linking of
the anionic polymers.
[0022] Furthermore, the coating layer is preferably laminated on top of the aluminum foil
layer by further applying a coating composition (Y), which comprises a cationic polymer
and a cross-linking agent that causes cross-linking of the cationic polymers, onto
the layer (M), and subsequently drying the coating composition (Y) to form a layer
(Y).
Moreover, the coating composition (M) and the coating composition (Y) preferably have
a relationship that satisfies an expression 2 ≥ (x'+y')/a' among a total mass (a')
(g) of the rare earth element-based oxide, and the phosphoric acid or the phosphate,
a total mass (x') (g) of the anionic polymer and the cross-linking agent that causes
cross-linking of the anionic polymers, and a total mass (y') (g) of the cationic polymer
and the cross-linking agent that causes cross-linking of the cationic polymers.
EFFECT OF THE INVENTION
[0023] The present invention is able to realize a packing material for a lithium cell that
has no impact from an environmental perspective, enables a simplification of the production
steps, and exhibits excellent electrolyte solution resistance, hydrofluoric acid resistance
and water resistance, as well as a production method for the packing material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024]
FIG. 1 is a cross-sectional view illustrating one example of a packing material for
a lithium cell according to the present invention.
FIG. 2 is a cross-sectional view illustrating another example of a packing material
for a lithium cell according to the present invention.
FIG. 3 is a cross-sectional view illustrating another example of a packing material
for a lithium cell according to the present invention.
FIG. 4 is a cross-sectional view illustrating another example of a packing material
for a lithium cell according to the present invention.
FIG. 5 is a cross-sectional view illustrating one example of a packing material for
a lithium cell according to the present invention that includes a dry laminate structure.
FIG. 6 is a cross-sectional view illustrating another example of a packing material
for a lithium cell according to the present invention that includes a dry laminate
structure.
FIG. 7 is a cross-sectional view illustrating another example of a packing material
for a lithium cell according to the present invention that includes a dry laminate
structure.
FIG. 8 is a cross-sectional view illustrating another example of a packing material
for a lithium cell according to the present invention that includes a dry laminate
structure.
DESCRIPTION OF THE REFERENCE SYMBOLS
[0025] 10, 20, 30, 40: Packing material for a lithium cell, 11: Base material layer, 12:
First adhesive layer, 13: Aluminum foil layer, 14: Coating layer, 14a: Layer (A),
14x: Layer (X), 14y: Layer (Y), 14m: Layer (M), 15: Adhesive resin layer, 15a: Second
adhesive layer, and 16: Sealant layer
BEST MODE FOR CARRYING OUT THE INVENTION
[0026] A more detailed description of the present invention is presented below.
[First Embodiment]
[0027] FIG. 1 is a cross-sectional view illustrating a first embodiment of a packing material
for a lithium cell according to the present invention. The lithium cell packing material
10 illustrated in FIG. 1 includes a first adhesive layer 12, an aluminum foil layer
13, a coating layer 14, an adhesive resin layer 15, and a sealant layer 16 laminated
sequentially on one surface of a base material layer 11.
<Coating Layer>
[0028] The coating layer 14 shown in FIG. 1 is a multilayer structure including a layer
(A) 14a, in which 1 to 100 parts by mass of a phosphoric acid or a phosphate has been
blended into 100 parts by mass of a rare earth element-based oxide (hereafter, this
layer is frequently referred to as "layer (A)"), and a layer (X) which contains an
anionic polymer and a cross-linking agent that causes cross-linking of the anionic
polymers (hereafter, this layer is frequently referred to as "layer (X)").
[0029] The lithium cell packing material should preferably be investigated with due consideration
of all manner of situations.
For example, many outer jacket materials for lithium cells are formed using cold molding
methods. Minor defects or pinholes or the like generated as a result of friction between
the molding die and the adhesive resin layer / sealant layer during the molding process
may potentially allow the aluminum foil layer that functions as an intermediate layer
within the lithium cell packing material to make direct contact with the electrolyte
solution. Accordingly, an action that protects the aluminum foil under more severe
evaluation conditions is desirable.
As a result of performing intensive investigation relating to the corrosion of aluminum
foils, the inventors of the present invention discovered that a rare earth element-based
oxide could be used as a material that yielded a corrosion prevention effect (inhibiter
effect) for aluminum foil that was similar to the effect obtained by conducting a
conventional chromate treatment, and yet was also environmentally favorable.
(Rare Earth Element-Based Oxide)
[0030] Examples of the rare earth element-based oxide include cerium oxide, yttrium oxide,
neodymium oxide and lanthanum oxide. Of these, cerium oxide is preferred.
In the present invention, during formation of the layer (A) 14a, a phosphoric acid
or a phosphate may be used as a dispersion stabilizer, so that the rare earth element-based
oxide is dispersed in a stable manner to form a sol-like state (a rare earth element-based
oxide sol). In this type of case, a rare earth element-based oxide sol in which the
average particle size is not more than 100 nm is preferred. In the rare earth element-based
oxide sol, various solvents such as water-based solvents, alcohol-based solvents,
hydrocarbon-based solvents, ketone-based solvents, ester-based solvents or ether-based
solvents may be used, although using a water-based rare earth element-based oxide
sol is particularly desirable.
[0031] As the dispersion stabilizer mentioned above, besides a phosphoric acid or a phosphate,
other inorganic acids such as nitric acid and hydrochloric acid, and organic acids
such as acetic acid, malic acid, ascorbic acid or lactic acid may also be used, although
a phosphoric acid or a phosphate is particularly preferred as the dispersion stabilizer.
By using a phosphoric acid or a phosphate as the dispersion stabilizer, not only can
the rare earth element-based oxide be dispersed in a stable manner, but other advantages
can also be expected, including an improvement in the adhesion to the aluminum foil
due to the aluminum chelating ability of the phosphoric acid, improved electrolyte
solution resistance due to capture of aluminum ions eluted under the effect of hydrofluoric
acid (that is, formation of a passive state), and an improvement in the cohesive strength
of the layer (A) 14a due to the fact that dehydration condensation of the phosphoric
acid occurs readily even at low temperatures. As a result of this improvement in the
cohesive strength, the strength properties of the lithium cell packing material also
tend to improve.
[0032] Examples of the phosphoric acid or phosphoric acid compound such as a phosphate include
orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, and alkali metal salts
or ammonium salts of these phosphoric acids. Further, various other salts such as
aluminum phosphate and titanium phosphate may also be used. Moreover, condensed phosphoric
acids such as trimetaphosphoric acid, tetrametaphosphoric acid, hexametaphosphoric
acid and ultrametaphosphoric acid, and the alkali metal salts or ammonium salts of
these condensed phosphoric acids (namely, condensed phosphates) are particularly preferred
in terms of the functions obtained. Particularly in those cases where the layer (A)
14a is formed using a sol-like rare earth element-based oxide (that is, a rare earth
element-based oxide sol), if due consideration is given to the dry film formation
properties (namely, the drying capabilities and the amount of heat required), then
a dispersion stabilizer that exhibits excellent reactivity at low temperatures is
preferred. Accordingly, in terms of the phosphate salt, Na ion salts are particularly
desirable as they exhibit excellent dehydration condensation properties at low temperature.
Furthermore, water-soluble salts are preferred.
[0033] The layer (A) 14a is formed by blending 1 to 100 parts by mass of the phosphoric
acid or phosphate with 100 parts by mass of the rare earth element-based oxide mentioned
above. The blend amount of the phosphoric acid or phosphate is preferably within a
range from 5 to 50 parts by mass, and is more preferably from 5 to 20 parts by mass.
If the blend amount of the phosphoric acid or phosphate is smaller than the lower
limit of the above-mentioned range, then the stability of the resulting rare earth
element-based oxide sol tends to deteriorate, and the functionality of the layer tends
to be inadequate for a lithium cell packing material. In contrast, if the blend amount
is greater than the upper limit of the above range, then the functionality of the
rare earth element-based oxide sol tends to decrease.
As described above, in those cases where a phosphate is used as the dispersion stabilizer,
a Na ion salt is preferred as the phosphate salt, but if the blend amount of the phosphate
exceeds the upper limit of the above-mentioned range, then needless to say, the types
of problems described above will occur.
[0034] In this manner, by blending a phosphorus compound with the rare earth element-based
oxide, not only can the dispersion of the rare earth element-based oxide be stabilized,
but an inhibitor effect that suppresses corrosion of the aluminum foil can also be
obtained. Furthermore, adhesion of the phosphoric acid compound to the aluminum foil
can also be improved, and a synergistic effect yields favorable electrolyte solution
resistance.
[0035] According to the present invention, because the coating layer 14 includes the aforementioned
layer (A) 14a, a typical coating method can be used to obtain a corrosion inhibiting
effect for metal foils such as aluminum foil, without the use of environmental toxins
such as hexavalent chromium.
[0036] However, in usual chemical conversion treatments typified by chromate treatments,
a graded structure is formed between the aluminum foil layer and the chemical conversion
treatment layer. As a result, the aluminum foil is often treated using a chemical
conversion treatment agent containing a blend of hydrofluoric acid, hydrochloric acid,
nitric acid, sulfuric acid, or salts of these acids, meaning both chromium-based and
non-chromium-based compounds act upon the aluminum foil to form the chemical conversion
treatment layer on the foil. One example of the chemical conversion treatment is a
phosphoric acid chromate treatment, and the basic principles of this treatment are
the same regardless of whether a dipping treatment or a coating treatment using a
resin binder is performed. However, because these chemical conversion treatment agents
use acids, they tend to cause corrosion of the operating environment and the coating
apparatus.
In contrast, with the type of coating layer described above that is used in the present
invention, a graded structure need not be formed on the aluminum foil, and in that
regard, the layer differs from the normal definition of a chemical conversion treatment.
As a result, there are no particular restrictions on the state of the coating agent,
which may be acidic, alkaline or neutral.
(Anionic Polymer)
[0037] As a result of performing intensive investigation using all manner of compounds with
the aim of improving resistances such as the electrolyte solution resistance and hydrofluoric
acid resistance to the levels required for a packing material for a lithium cell 10,
the inventors of the present invention discovered that anionic polymers improved the
stability of the layer (A). Examples of the effects achievable include protecting
the hard and brittle layer (A) with an acrylic resin component, and trapping ion contaminants
derived from the phosphate contained within the rare earth element-based oxide sol
(and particularly contaminants derived from Na ions) (namely, a cation catcher).
As a general principle not restricted to lithium cell packing material applications,
if a protective layer provided for the purpose of preventing corrosion of an aluminum
foil by corrosive compounds contains ion contaminants, and particularly alkali metal
ions or alkaline earth metal ions such as Na ions, then these ion contaminants tend
to act as the start points for damage of the protective layer. Accordingly, using
an anionic polymer to solidify ion contaminants such as Na ions contained within the
rare earth element-based oxide sol is effective in improving the durability of the
lithium cell packing material.
[0038] Examples of the anionic polymer include polymers containing carboxyl groups, and
specific examples thereof include poly(meth)acrylic acids and salts thereof, and copolymers
that include (meth)acrylic acid or a salt thereof as a main component. Examples of
the components that may be copolymerized in such copolymers include alkyl (meth)acrylate
monomers having an alkyl group such as a methyl group, ethyl group, n-propyl group,
i-propyl group, n-butyl group, i-butyl group, t-butyl group, 2-ethylhexyl group or
cyclohexyl group; amide group-containing monomers such as (meth)acrylamide, N-alkyl
(meth)acrylamides and N,N-dialkyl (meth)acrylamides (wherein examples of the alkyl
group include a methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl
group, i-butyl group, t-butyl group, 2-ethylhexyl group or cyclohexyl group), N-alkoxy
(meth)acrylamides and N,N-dialkoxy (meth)acrylamides (wherein examples of the alkoxy
group include a methoxy group, ethoxy group, butoxy group or isobutoxy group), N-methylol
(meth)acrylamide, and N-phenyl (meth)acrylamide; hydroxyl group-containing monomers
such as 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate; glycidyl
group-containing monomers such as glycidyl (meth)acrylate and allyl glycidyl ether;
silane-containing monomers such as (meth)acryloxypropyltrimethoxysilane and (meth)acryloxypropyltriethoxysilane;
and isocyanate group-containing monomers such as (meth)acryloxypropyl isocyanate.
[0039] As described above, the anionic polymers are effective materials for lithium cell
packing materials, and by combining the layer (X) containing the anionic polymer with
the layer (A) described above, even greater improvements in functionality can be expected.
However, if consideration is given to the fact that the lithium cell packing material
is dipped in water during evaluation of the water resistance, then the coating layer
14 requires water resistance and water-resistant adhesiveness to act as an anchor
coating agent. Although an anionic polymer containing anionic groups such as carboxylic
groups is effective in terms of the trapping of ion contaminants within the layer
(A) containing rare earth element-based oxides, because it is water-based, the use
of an anionic polymer by itself tends to result in inferior water resistance.
[0040] As a result of performing intensive investigation relating to the issue of delamination
due to water immersion after the electrolyte evaluation, its were paid attention to
by the inventors of the present invention as the reasons of the poor water resistance
of the anionic polymer that the anionic polymer can be dissolved in water and the
water resistance of the adhesive interface is poor. In addition, as the solutions
of the aforementioned reasons, the addition of a cross-linking agent is exemplified
for the former reason, and the formation of the interaction at the adhesive interface
is exemplified for the latter reason. Because one of the reasons of the latter reason
is the former reason, it was found that the latter reason is solved by solving the
former reason. On the basis of these findings, the solution of the problem of water
resistance was found.
(Cross-Linking Agent)
[0041] Examples of the cross-linking agent used for converting the anionic polymers to a
cross-linked structure include at least one material selected from the group consisting
of compounds having an isocyanate group, a glycidyl group, a carboxyl group or an
oxazoline group as a functional group, and silane coupling agents.
Examples of compounds having an isocyanate group include diisocyanates such as tolylene
diisocyanate, xylylene diisocyanate, and hydrogenation products thereof; hexamethylene
diisocyanate, 4,4'-diphenylmethane diisocyanate and hydrogenation products thereof;
and isophorone diisocyanate; as well as adducts prepared by reacting the above isocyanates
with a polyhydric alcohol such as trimethylolpropane, and biurets obtained by reacting
the above isocyanates with water; polyisocyanates such as isocyanurates (which are
trimers), and blocked polyisocyanates in which these polyisocyanates are blocked with
an alcohol, a lactam or an oxime or the like.
Examples of compounds having a glycidyl group include epoxy compounds obtained by
the interaction between a glycol such as ethylene glycol, diethylene glycol, triethylene
glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol,
polypropylene glycol, 1,4-butanediol, 1,6-hexanediol or neopentyl glycol, and epichlorohydrin;
epoxy compounds obtained by the interaction between a polyhydric alcohol such as glycerol,
polyglycerol, trimethylolpropane, pentaerythritol or sorbitol, and epichlorohydrin;
and epoxy compounds obtained by the interaction between a dicarboxylic acid such as
phthalic acid, terephthalic acid, oxalic acid or adipic acid, and epichlorohydrin.
Examples of compounds having a carboxyl group include the various aliphatic or aromatic
dicarboxylic acids, as well as poly(meth)acrylic acids, and alkali (or alkaline earth)
metal salts of poly(meth)acrylic acids.
Examples of compounds having an oxazoline group include low molecular weight compounds
having two or more oxazoline units. Furthermore, in those cases where a polymerizable
monomer such as isopropenyloxazoline is used, a copolymer prepared by copolymerization
with an acrylic monomer such as (meth)acrylic acid, an alkyl (meth)acrylate or a hydroxyalkyl
(meth)acrylate or the like may also be used.
[0042] Moreover, as the cross-linking agent, the use of a silane coupling agent that is
capable of causing a selective reaction between the amines and the functional groups,
and making the cross-linking points be siloxane bonds, is preferred. Examples of the
silane coupling agent include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane,
β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-chloropropylmethoxysilane, vinyltrichlorosilane,
γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane,
and γ-isocyanatopropyltriethoxysilane. Considering the level of reactivity with the
cationic polymer or copolymer thereof, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,
γ-aminopropyltriethoxysilane or γ-isocyanatopropyltriethoxysilane is particularly
desirable.
[0043] The cross-linking agent is typically added in an amount within a range from 1 to
50 parts by mass per 100 parts by mass of the anionic polymer. If the blend amount
of the cross-linking agent is less than the lower limit of the above-mentioned range,
then the amount of cross-linking structures may be insufficient. In contrast, if the
blend amount is greater than the upper limit of the above range, then the pot life
of the coating liquid may deteriorate.
A single cross-linking agent may be used, or two or more different cross-linking agents
may be used in combination. Further, combinations of a cross-linking agent and a silane
coupling agent may also be used.
[0044] As described above, the anionic polymer is a material that is extremely effective
in capturing ion contaminants. Furthermore, by adding a cross-linking agent to each
polymer, the water resistance can also be improved. Accordingly, by providing a layer
(X) 14x containing an anionic polymer as illustrated in FIG. 1, the electrolyte solution
resistance, the hydrofluoric acid resistance and the water resistance of the coating
layer 14 can be further improved.
However, the type of anionic polymer-containing layer (X) 14x described above have
no function for protecting the aluminum foil from corrosion. Hence, as shown in FIG.
1, by forming the coating layer 14 as a multilayer structure containing the layer
(A) 14a in addition to the layer (X) 14x, a corrosion prevention effect can be obtained
for metal films such as an aluminum foil.
[0045] Although described in further detail below, the layer (A) 14a is preferably laminated
directly onto the aluminum foil layer 13, as illustrated in FIG. 1. Further, because
the layer (A) 14a is formed using a sol-like material in which the rare earth element-based
oxide has been stably dispersed using a phosphoric acid or a phosphate (namely, a
rare earth element-based oxide sol), the layer (A) 14a essentially becomes a structure
in which sol particles of the rare earth element-based oxide are closely packed. In
contrast, the layer (X) 14x is laminated on top of the layer (A) 14a, and fills any
gaps between the closely packed rare earth element-based oxide sol particles. In other
words, the coating composition (X) that forms the layer (X) 14x is coated onto the
layer (A) 14a while penetrating into any gaps within the layer (A) 14a, thus forming
the layer (X) 14x. During this process, the coating composition (X) that penetrates
into the gaps in the layer (A) 14a undergoes thermal cross-linking, meaning the layer
(X) 14x also has a protective layer type effect for the layer (A) 14a.
[0046] In order to enable the layer (X) 14x to exhibit a more effective protective layer
type role for the layer (A) 14a, the relationship between the mass (a) per unit surface
area (g/m
2) of the layer (A), and the mass (x) per unit surface area (g/m
2) of the layer (X) preferably satisfies the expression 2 ≥ x/a.
If this relationship (x/a) between the mass values for each layer exceeds the above-mentioned
range, then although the layer (X) 14x is still able to perform a protective layer
type role for the layer (A) 14a, the proportion of the layer (X) 14x laminated on
top of the layer (A) 14a, in addition to the coating composition (X) that fills the
gaps in the layer (A) 14a, tends to increase more than is necessary. Rather than existing
in isolation, the anionic polymer within the layer (X) 14x tends to exhibit more effective
functionality such as electrolyte solution resistance and hydrofluoric acid resistance
when complexed with the rare earth element-based oxide and the phosphoric acid or
phosphate contained within the layer (A) 14a. Accordingly, if the relationship ( x
/a) between the mass values for each layer exceeds the above-mentioned range, then
the proportion of the anionic polymer that does not form a complex with the rare earth
element-based oxide and the phosphoric acid or phosphate contained within the layer
(A) 14a, but rather exists in isolation, tends to increase, meaning the desired functions
of electrolyte solution resistance and hydrofluoric acid resistance may not manifest
satisfactorily, resulting in deterioration in the electrolyte solution resistance
and the hydrofluoric acid resistance. Furthermore, because the coating amount of the
coating composition (X) increases, the composition may become more difficult to cure.
The drying temperature could simply be set higher or the curing time extended in order
to ensure satisfactory curing of the coating composition (X), but this tends to result
in a fall in productivity. Accordingly, in terms of maintaining productivity levels,
while also ensuring a favorable improvement in the electrolyte solution resistance
and the hydrofluoric acid resistance, the relationship (x/a) between the mass values
for each layer preferably satisfies 2 ≥ x/a, more preferably satisfies 1.5 ≥ x/a ≥
0.01, and most preferably satisfies 1.0 ≥ x/a ≥ 0.1.
The above relationship is based on the mass values for each layer, but provided the
specific gravity can be determined for each layer, the relationship may also be reported
in terms of the thickness of the coating layer 14. The thickness of the coating layer
14 is not particularly restricted as long as the aforementioned relationship is satisfied,
and is preferably within a range from 0.01 to 10 µm, for example.
[0047] The mass (a) per unit surface area of the layer (A) 14a is preferably within a range
from 0.010 to 0.200 g/m
2, and is more preferably from 0.040 to 0.100 g/m
2. If this mass (a) is less than the lower limit of the above-mentioned range, then
the absolute amounts of the rare earth element-based oxide having the aluminum foil
corrosion inhibiting effect, and the phosphoric acid or phosphate become too small,
and achieving the desired electrolyte solution resistance and hydrofluoric acid resistance
may be difficult. On the other hand, if the mass (a) is greater than the upper limit
of the above range, then the sol-gel reaction that accompanies drying of the rare
earth element-based oxide sol used in the present invention tends to proceed poorly
(in other words, insufficient heat causes the sol-gel reaction to proceed poorly),
and the cohesive strength of the rare earth element-based oxide sol tends to decrease,
causing deterioration in the strength properties when used as a packing material for
a lithium cell. Accordingly, provided the mass (a) per unit surface area of the layer
(A) 14a is within the above-mentioned range, electrolyte solution resistance is maintained,
and the cohesive strength of the rare earth element-based oxide sol can be maintained,
thus ensuring the level of strength required for a lithium cell packing material.
<Aluminum Foil Layer>
[0048] Typical flexible aluminum foil may be used as the material for the aluminum foil
layer, although in order to ensure more favorable pinhole resistance and impart superior
spreadability during molding, the use of an aluminum foil that contains iron is preferred.
The iron content within 100% by mass of the aluminum foil is preferably within a range
from 0.1 to 9.0% by mass, and is more preferably from 0.5 to 2.0% by mass. If the
iron content is less than the lower limit of the above-mentioned range, then the desired
levels of pinhole resistance and spreadability may not be achieved, whereas if the
iron content is greater than the upper limit of the above range, then the flexibility
of the foil may be lost.
Further, considering factors such as the barrier properties, pinhole resistance and
workability, the thickness of the aluminum foil layer 13 shown in FIG. 1 is preferably
within a range from 9 to 200 µm, and is more preferably from 15 to 100 µm.
[0049] As the aluminum foil, an untreated aluminum foil may be used, but in terms of imparting
superior resistance to the electrolyte solution, the use of an aluminum foil that
has undergone a degreasing treatment is preferred. Degreasing treatments can be broadly
classified as wet or dry treatments.
Examples of wet treatments include acid degreasing and alkali degreasing treatments.
Examples of the acids used in acid degreasing include inorganic acids such as sulfuric
acid, nitric acid, hydrochloric acid and hydrofluoric acid, and these acids may be
used individually or in combinations of two or more different acids. Further, from
the viewpoint of improving the etching effect of the aluminum foil, various metal
salts that can act as supply sources for Fe ions or Ce ions may also be added if required.
Examples of the alkali used in alkali degreasing include powerful etching type alkalis
such as sodium hydroxide. Further, treatment agents containing weaker alkalis or surfactants
or the like may also be used. These degreasing treatments are conducted by dipping
methods or spraying methods.
One example of a dry treatment is a degreasing treatment conducted by annealing the
aluminum.
Furthermore, in addition to the treatments described above, other degreasing treatments
include flame treatments and corona treatments. Moreover, degreasing treatments in
which active oxygen generated by the irradiation of ultraviolet light of a specific
wavelength is used to oxidatively decompose and remove contaminants may also be used.
[0050] In the present invention, a satisfactory level of electrolyte solution resistance
can be imparted with a dry degreasing treatment, and there is no necessity to perform
the type of wet degreasing treatments or etching level treatments described above.
In other words, the annealing treatment performed to improve the flexibility of the
aluminum foil yields a simultaneous degreasing treatment action that is able to impart
satisfactory electrolyte solution resistance to the foil. As mentioned above, this
characteristic is due to the fact that the coating layer 14 is a multilayer structure
including the layer (A) 14a and the layer (X) 14x. This effect is particularly pronounced
when a rare earth element-based oxide sol that has been stably dispersed using phosphoric
acid or a phosphate is used as the rare earth element-based oxide.
<Adhesive Resin Layer>
[0051] The structures illustrated in FIG. 1 to FIG. 4 are structures that have an adhesive
resin layer 15 provided between the coating layer 14 and the sealant layer 16, and
are produced by either an extrusion lamination method or a thermal lamination method.
The adhesive resin layer 15 is preferably composed of (i) or (ii) below. Furthermore,
the thickness of the adhesive resin layer 15 is preferably within a range from 1 to
40 µm, and is more preferably from 5 to 20 µm.
- (i) an acid-modified polyolefin-based resin (α).
- (ii) a resin composition in which an acid-modified polyolefin-based resin (α) (30
to 99% by mass) is combined with an isocyanate compound or derivative thereof (β)
and a silane coupling agent (γ) ((β) + (γ): 1 to 70% by mass), provided that the mass
ratio between the isocyanate compound or derivative thereof (β) and the silane coupling
agent (γ), for the case where (β) + (γ) is deemed to be 100, satisfies (β) : (γ) =
10 to 90 : 90 to 10. It should be noted that (α) + {(β) + (γ)} = 100% by mass.
[0052] In those cases where the adhesive resin layer 15 is of the above structure (ii),
if the proportion of the acid-modified polyolefin-based resin (α) exceeds 99% by mass,
then the electrolyte solution resistance tends to deteriorate, whereas if the proportion
is less than 30% by mass, then the adhesion to the sealant layer 16 described below
tends to deteriorate. The proportion of the acid-modified polyolefin-based resin (α)
is preferably within a range from 60 to 80% by mass.
On the other hand, if the mass ratio between the isocyanate compound or derivative
thereof (β) and the silane coupling agent (γ) falls outside the above-mentioned range,
then the electrolyte solution resistance tends to worsen. The mass ratio (β) : (γ)
is preferably 50 to 80 : 80 to 50.
[0053] As the acid-modified polyolefin-based resin (α), an acid-modified polyolefin resin
produced by grafting maleic anhydride or the like onto a polyolefin resin is preferred.
Examples of the polyolefin resin include low-density, medium-density and high-density
polyethylene; copolymers of ethylene and an α-olefin; homo-, block or random polypropylenes;
and copolymers of propylene and an α-olefin. These polyolefin resins may be used individually
or in combinations of two or more different resins. Furthermore, the resin may be
used in the form of a dispersion within an organic solvent, and this facilitates the
blending of various additives effective in improving the adhesion, as well as the
isocyanate compound or derivative thereof (β) and the silane coupling agent (γ) described
below.
[0054] Examples of the isocyanate compound or derivative thereof (β) include diisocyanates
such as tolylene diisocyanate, xylylene diisocyanate, and hydrogenation products thereof;
hexamethylene diisocyanate, 4,4'-diphenylmethane diisocyanate and hydrogenation products
thereof; and isophorone diisocyanate; as well as adducts prepared by reacting the
above diisocyanates with a polyhydric alcohol such as trimethylolpropane, and biurets
obtained by reacting the above diisocyanates with water; polyisocyanates such as isocyanurates
(which are trimers), and blocked polyisocyanates in which these polyisocyanates are
blocked with an alcohol, a lactam or an oxime or the like.
These isocyanate compounds or derivatives thereof (β) may be used in either an organic
solvent-based form or a water-based form.
[0055] Examples of the silane coupling agent (γ) include vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane,
γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, γ-glycidoxypropyltrimethoxysilane,
γ-glycidoxypropyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-chloropropylmethoxysilane,
vinyltrichlorosilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane,
N-P-(aminoethyl)-γ-aminopropyltrimethoxysilane, and γ-isocyanatopropyltriethoxysilane.
The silane coupling agent (γ) preferably contains functional groups that exhibit favorable
reactivity with the acid-modified polyolefin-based resin (α). From this viewpoint,
the use of an epoxysilane or aminosilane as the silane coupling agent (γ) is preferred,
and an isocyanatosilane may also be used, although the reactivity tends to be lower.
<Adhesive Layer>
[0056] The structures illustrated in FIG. 5 to FIG. 8 are structures that have a second
adhesive layer 15a provided between the coating layer 14 and the sealant layer 16,
and are produced by a dry lamination method. Examples of the material used for the
second adhesive layer 15a, and for the first adhesive layer 12 provided between the
base material layer 11 and the aluminum foil layer 13 in FIG. 1 to FIG. 4, include
polyurethane-based adhesives containing any of various polyols as the main component,
and containing an isocyanate compound or derivative thereof as a curing agent component.
Examples of the polyol that functions as the main component include polyester polyols,
polyether polyols, polycarbonate polyols, acrylic polyols, and polyolefin polyols.
Specific examples of polyester polyols include compounds obtained using one or more
aliphatic dibasic acids such as succinic acid, glutaric acid, adipic acid, pimelic
acid, suberic acid, azelaic acid, sebacic acid or brassylic acid, and/or aromatic
dibasic acids such as isophthalic acid, terephthalic acid or naphthalenedicarboxylic
acid, with one or more aliphatic diols such as ethylene glycol, propylene glycol,
butanediol, neopentyl glycol, methylpentanediol, hexanediol, heptanediol, octanediol,
nonanediol, decanediol or dodecanediol, and/or alicyclic diols such as cyclohexanediol
or hydrogenated xylylene glycol, and/or aromatic diols such as xylylene glycol. Furthermore,
polyurethane polyols in which chain extensions have been performed at hydroxyl groups
within the above polyols using an isocyanate compound may also be used.
Examples of the isocyanate compound or derivative thereof that functions as the curing
agent component include the same materials as those listed above in the section relating
to the <adhesive resin layer>. Usually, a polyurethane-based adhesive used for a dry
lamination process need only include the above main component and curing agent in
the basic composition, although other additives may also be added to improve various
adhesion properties or impart various resistance properties. Examples of these additives
include carbodiimide compounds, oxazoline compounds, epoxy compounds, phosphorus-based
compounds, and silane coupling agents.
The thicknesses of the first adhesive layer 12 and the second adhesive layer 15a shown
in FIG. 1 to FIG. 8 are preferably within a range from 1 to 10 µm, and more preferably
from 3 to 7 µm. Further, the first adhesive layer 12 and the second adhesive layer
15a may be composed of the same type of polyurethane-based adhesive, or may be composed
of different polyurethane-based adhesives.
<Sealant Layer>
[0057] Examples of the components that constitute the sealant layer 16 illustrated in FIG.
1 include polyolefin resins, and acid-modified polyolefin resins produced by grafting
maleic anhydride or the like onto a polyolefin resin. The polyolefin resin may use
one or more resins selected from the various polyolefin resins exemplified above in
the description relating to the adhesive resin layer.
Further, the sealant layer 16 may be a single layer film, or a multilayer film produced
by laminating a plurality of layers together. For example, depending on the functionality
required, a multilayer film containing an interposed film of a resin such as an ethylene-cyclic
olefin copolymer or a polymethylpentene may be used to impart improved moisture resistance.
Furthermore, various additives may also be blended into the sealant layer 16, including
flame retardants, slip agents, anti-blocking agents, antioxidants, photostabilizers
and tackifiers.
The thickness of the sealant layer 16 is preferably within a range from 10 to 100
µm, and is more preferably from 20 to 50 µm.
<Base Material Layer>
[0058] The base material layer 11 illustrated in FIG. 1 is provided for the purposes of
imparting heat resistance during the sealing step of the lithium cell production,
and preventing pinholes from occurring during processing or distribution. A resin
layer having insulating properties is preferably used as the base material layer 11.
Examples of resins that may be used include oriented or non-oriented polyester films,
polyamide films and polypropylene films. Further, these films may be used as a single
layer, or as a multilayer film prepared by laminating two or more layers. In terms
of improving properties such as the moldability, heat resistance, pinhole resistance
and insulation, an oriented polyamide film or oriented polyester film is ideal.
The thickness of the base material layer 11 is preferably within a range from 6 to
40 µm, and is more preferably from 10 to 25 µm. If the thickness of the base material
layer 11 is less than the above-mentioned range, then the pinhole resistance and insulation
properties tend to deteriorate. In contrast, if the thickness exceeds the above range,
then the layer becomes difficult to mold.
<Production Method for Packing Material for Lithium Cell>
[0059] Next is a description of a production method for the lithium cell packing material
10 of the present invention illustrated in FIG. 1, although the present invention
is not restricted to the production method described below.
(Lamination of Coating Layer to Aluminum Foil Layer)
[0060] It is preferable that the layer (A) 14a of the coating layer 14 be laminated directly
onto the aluminum foil layer 13. By laminating the layer (A) 14a directly onto the
aluminum foil layer 13, corrosion of the aluminum foil layer 13 can be prevented well.
Therefore, firstly, a coating composition (A) containing a rare earth element-based
oxide and a phosphoric acid or phosphate in an amount of 1 to 100 parts by mass per
100 parts by mass of the rare earth element-based oxide is coated onto the aluminum
foil layer 13, and subsequently subjected to drying, curing and baking to form the
layer (A) 14a. Next, a coating composition (X) containing an anionic polymer and a
cross-linking agent that causes cross-linking of the anionic polymers is coated onto
the layer (A) 14a, and subsequently subjected to drying, curing and baking to form
the layer (X) 14x.
In this manner, a coating layer 14 composed of the layer (A) 14a and the layer (X)
14x is laminated on top of the aluminum foil layer 13.
The coating composition (A) contains the phosphoric acid or phosphate as a sol stabilizer.
By utilizing this phosphoric acid or phosphate, additional functionality, namely an
improved aluminum corrosion prevention effect can be expected.
[0061] In terms of the coating method, conventional methods may be used, including gravure
coaters, gravure reverse coaters, roll coaters, reverse roll coaters, die coaters,
bar coaters, kiss coaters and comma coaters.
As described above, the aluminum foil layer 13 may use either an untreated aluminum
foil, or an aluminum foil that has been subjected to a wet or dry degreasing treatment.
(Bonding of Base Material Layer and Aluminum Foil Layer)
[0062] The aluminum foil layer 13 having the coating layer 14 laminated thereon, and the
base material layer 11 are bonded together. Using dry lamination, non-solvent lamination
or wet lamination or the like as the bonding method, the two components are bonded
together using the adhesive described above, thus preparing a laminate having a structure
represented by base material layer 11 / first adhesive layer 12 / aluminum foil layer
13 / coating layer 14.
(Lamination of Sealant Layer)
[0063] The sealant layer 16 is laminated on top of the laminate described above. Examples
of the method used for this lamination include dry processes and wet processes.
In the case of a dry process, an adhesive resin is extrusion laminated onto the surface
of the coating layer 14 of the laminate, and the sealant layer 16 that has been prepared
by an inflation method or casting method is then laminated onto the adhesive resin,
thus producing the lithium cell packing material 10. The coating layer 14 may be provided
in-line during the above extrusion lamination process. Subsequently, a heat treatment
(such as an aging treatment or thermal lamination treatment) may be performed to improve
the adhesion between the coating composition and the adhesive resin, although in the
present invention, by employing the type of layered structure described above, a lithium
cell packing material 10 having excellent adhesion can be obtained with the small
amount of heat applied during the extrusion lamination.
Furthermore, an inflation method or casting method may be used to prepare a multilayer
film composed of the adhesive resin and the sealant layer 16, with this multilayer
film then laminated onto the above laminate via a thermal lamination process.
[0064] In the case of a wet process, a dispersion of the acid-modified polyolefin-based
resin (α) is coated onto the surface of the coating layer 14 of the above laminate,
the solvent is volatilized at a temperature not less than the melting point of the
acid-modified polyolefin-based resin (α), thereby melt-softening and baking the resin.
Subsequently, the sealant layer 16 is laminated via a heat treatment such as thermal
lamination, thus producing the lithium cell packing material 10.
Examples of the coating method include the various coating methods exemplified above
in the description of the lamination of the coating layer to the aluminum foil layer.
[Second Embodiment]
[0065] FIG. 2 is a cross-sectional view illustrating a second embodiment of a lithium cell
packing material 20 according to the present invention. This embodiment is described
below in detail. In FIG. 2, those structural components that are the same as those
in FIG. 1 are labeled using the same symbols, and description of these identical components
may be omitted.
<Coating Layer>
[0066] The coating layer 14 of the embodiment shown in FIG. 2 is a multilayer structure
further including, in addition to a layer (A) 14a and a layer (X) 14x, a layer (Y)
14y containing a cationic polymer and a cross-linking agent that causes cross-linking
of the cationic polymers (hereafter, this layer is referred to as "layer (Y)").
In the embodiment shown in FIG. 2, there is illustrated the multilayer structure in
which the layer (A) 14a, the layer (X) 14x, and the layer (Y) 14y are laminated on
the aluminum foil layer 13 in this order, but the layer (X) 14x and the layer (Y)
14y can be exchanged. Also, the aforementioned layer (A) and layer (X) are the same
as the layer (A) and the layer (X) described in the first embodiment.
(Cationic Polymer)
[0067] As a result of further intensive investigation, the inventors of the present invention
discovered that cationic polymers exhibited particularly excellent electrolyte solution
resistance and hydrofluoric acid resistance. It is surmised that the reasons for these
superior resistance properties include the trapping of fluorine ions by the cationic
groups (namely, an anion catcher), thereby suppressing damage to the aluminum foil
that is an intermediate layer of a packing material for a lithium cell.
[0068] Examples of the cationic polymer include polymers that contain amines, and of such
polymers, polyethyleneimines, ionic polymer complexes made of a polyethyleneimine
and a polymer having carboxylic acid groups, primary amine-grafted acrylic resins
having a primary amine grafted to the main acrylic backbone, polyallylamines and derivatives
thereof, and aminophenols are preferred. Polyallylamines and derivatives thereof are
particularly desirable.
Examples of polymers having carboxylic acid groups that form ionic polymer complexes
with a polyethyleneimine include polycarboxylic acid (or salts) such as polyacrylic
acids or ion salts thereof, or copolymers obtained by introducing a comonomer into
such a polycarboxylic acid (or salt), and carboxyl group-containing polysaccharides
such as carboxymethylcellulose or ion salts thereof.
As the polyallylamine, homopolymers or copolymers of allylamine, allylamine amide
sulfate, diallylamine and/or dimethylallylamine and the like may be used. These amines
may be either free amines, or stabilized amines that have been stabilized using acetic
acid or hydrochloric acid. Furthermore, maleic acid or sulfur dioxide or the like
may also be used as copolymer components. Moreover, polymers in which a portion of
the primary amines have been methoxylated to impart thermal cross-linking properties
may also be used.
In the case of an aminophenol, compounds in which a portion of the primary amines
have been methoxylated to impart thermal cross-linking properties may also be used.
Any of these cationic polymers may be used individually, or two or more different
polymers may be used in combination.
[0069] The cationic polymer is an extremely effective material as a trap for hydrofluoric
acid, and by combining the layer (Y) 14y containing the cationic polymer with the
layer (A) 14a and the layer (X) 14x described above, even greater improvements in
functionality can be expected. However, because a cationic polymer is water-based
in the same way as an anionic polymer, the use of a cationic polymer by itself tends
to result in inferior water resistance. Therefore, it is preferred that the layer
(Y) 14y contain cross-linking agents that cross-link the cationic polymers.
As cross-linking agents, it is possible to use at least one selected from the cross-linking
agents exemplified above in the first embodiment.
[0070] These cross-linking agents are typically added in an amount within a range from 1
to 50 parts by mass per 100 parts by mass of the cationic polymer. If the blend amount
of the cross-linking agent is less than the lower limit of the above-mentioned range,
then the amount of cross-linking may be insufficient. In contrast, if the blend amount
is greater than the upper limit of the above range, then the pot life of the coating
liquid may deteriorate.
In those cases where the cationic polymer is a polyallylamine derivative in which
the primary amines of the polyallylamine have been methoxycarbonylated, because the
polymer itself has thermal cross-linking properties, even if a cross-linking agent
is not added, the polymer still performs in the same manner as compositions containing
a cross-linking agent. Further, as for the method used for cross-linking the cationic
polymers and anionic polymers, methods that employ cross-linking agents other than
those described above may also be used, including methods that use a titanium or zirconium
compound as the cross-linking agent to form cross-linked structures such as ionic
cross-linking.
The cross-linking agents described above may be used individually, or two or more
different cross-linking agents may be used in combination. Further, combinations of
a cross-linking agent and a silane coupling agent may also be used.
[0071] As described above, the anionic polymer is extremely effective material as a trap
for ion contaminants, and the cationic polymer is extremely effective material as
a trap for hydrofluoric acid. Hence, as shown in FIG. 2, by forming the coating layer
14 as a multilayer structure containing the layer (Y) 14y in addition to the layer
(A) 14a and the layer (X) 14x, a corrosion prevention effect can be obtained for metal
films such as an aluminum foil, and the lithium cell packing material can be obtained
which exhibit improved levels of electrolyte solution resistance, hydrofluoric acid
resistance and water resistance.
[0072] Rather than each existing in isolation, the anionic polymer within the layer (X)
14x and the cationic polymer within the layer (B) 14b tends to exhibit more effective
functionality such as electrolyte solution resistance and hydrofluoric acid resistance
when complexed with the rare earth element-based oxide and the phosphoric acid or
phosphate contained within the layer (A) 14a. Accordingly, if the proportions of the
layer (X) 14x and the layer (Y) 14y, which are laminated on the layer (A) 14a as shown
in FIG. 13, increase more than necessary, then the proportions of the anionic polymer
and the cationic polymer that do not form a complex with the rare earth element-based
oxide and the phosphoric acid or phosphate contained within the layer (A) 14a, but
rather exist in isolation, tend to increase, meaning the desired functions of electrolyte
solution resistance and hydrofluoric acid resistance may not manifest satisfactorily,
resulting in deterioration in the electrolyte solution resistance and the hydrofluoric
acid resistance.
[0073] Therefore, in order to more efficiently exert the electrolyte solution resistance
and the hydrofluoric acid resistance, the relationship among the mass per unit
surface are
a a (g/m
2) of the layer (A), the mass per unit
surface are
a x (g/m
2) of the layer (X), and the mass per unit
surface are
a y (g/m
2) of the layer (Y) should satisfy 2
> (x+y)/a. Even in the case where the relationship among the masses of the respective
layers {(x+y)/a} exceed the above-mentioned range, then although the effects of the
present invention can still be obtained, the coating amounts of the coating composition
(X) and the coating composition (Y) that constitutes the layer (Y) tend to increase,
meaning the compositions may become more difficult to cure. The drying temperature
could simply be set higher or the curing time extended in order to ensure satisfactory
curing of the coating composition (X) and coating composition (Y), but this tends
to result in a fall in productivity.
Accordingly, in terms of maintaining productivity levels, while also ensuring a favorable
improvement in the electrolyte solution resistance and the hydrofluoric acid resistance,
the relationship {(x+y)/a} between the mass values for each layer preferably satisfies
2 ≥ (x+y)/a, more preferably satisfies 1.5 ≥ (x+y)/a ≥ 0.01, and most preferably satisfies
1.0 ≥ (x+y)/a > 0.1.
<Production Method for Packing Material for Lithium Cell>
[0074] Next is a description of a production method for the lithium cell packing material
20 of the present invention illustrated in FIG. 2, although the present invention
is not restricted to the production method described below.
[0075] In the step of laminating the coating layer onto the aluminum foil layer, the layer
(A) 14a and the layer (X) 14x are first formed on top of the aluminum foil layer 13
in the same manner as the method described for the first embodiment. Subsequently,
the coating composition (Y) containing the cationic polymer and the cross-linking
agent that causes cross-linking of the cationic polymers is coated onto the layer
(X) 14x, and is then subjected to drying, curing and baking to form the layer (Y)
14y. In this manner, a coating layer 14 composed of the layer (X) 14x and the layer
(Y) 14y is laminated on top of the aluminum foil layer 13.
The steps of bonding the base material layer to the aluminum foil layer, and laminating
the sealant layer are then conducted in the same manner as the production method for
the lithium cell packing material 10 described above, thus completing production of
the lithium cell packing material 20.
[0076] It is preferable that the layer (A) 14a of the coating layer 14 be laminated directly
onto the aluminum foil layer 13. Also, there is no particular restriction on the lamination
order of the layer (X) 14x and the layer (Y) 14y. As shown in FIG. 2, the multilayer
structure can contain the layer (A) 14a, the layer (X) 14x, and the layer (Y) 14y
laminated in this order, and the layer (X) 14x and the layer (Y) 14y can be exchanged.
Furthermore, the layer (A) 14a, the layer (X) 14x, and the layer (Y) 14y can be repeatedly
laminated according to need.
[Third Embodiment]
[0077] FIG. 3 is a cross-sectional view illustrating a third embodiment of a lithium cell
packing material 30 according to the present invention. This embodiment is described
below in detail. In FIG. 3, those structural components that are the same as those
in FIG. 1 are labeled using the same symbols, and description of these identical components
may be omitted.
<Coating Layer>
[0078] The coating layer 14 of the example shown in FIG. 3 has the single layer structure
comprised of the layer (M) 14m (hereinafter referred to as the "layer (M)") which
contains a rare earth element-based oxide, a phosphoric acid or phosphate, an anionic
polymer, and a cross-linking agent that causes cross-linking of the anionic polymers.
In the layer (M), the phosphoric acid or phosphate is contained in an amount of 1
to 100 parts by mass per 100 parts by mass of the rare earth element-based oxide.
[0079] The rare earth element-based oxide, and the phosphoric acid or phosphate are the
same as the rare earth element-based oxide and the phosphoric acid or phosphate described
in the first embodiment. Further, the anionic polymer and the cross-linking agent
that causes cross-linking of the anionic polymers are the same as the anionic polymer
and cross-linking agent described in the second embodiment.
[0080] As described above, the anionic polymer is a material that is extremely effective
in capturing ion contaminants. Furthermore, by adding a cross-linking agent to each
polymer, the water resistance can also be improved. Rather than existing in isolation,
the anionic polymer tend to exhibit more effective functionality such as electrolyte
solution resistance and hydrofluoric acid resistance when complexed with the rare
earth element-based oxide and the phosphoric acid or phosphate contained.
Accordingly, when the coating layer 14 is prepared as shown in FIG. 3 to be the layer
(M) 14 m which contains the anionic polymer, and the cross-linking agent in addition
to the rare earth element-based oxide having the function for protecting the aluminum
foil from corrosion, the phosphoric acid or phosphate, it is possible to obtain the
lithium cell packing material that is excellent in the electrolyte solution resistance,
the hydrofluoric acid resistance, and the water resistance while holding the corrosion
prevention effect for metal films such as an aluminum foil.
<Production Method for Packing Material for Lithium Cell>
[0081] Next is a description of a production method for the lithium cell packing material
30 of the present invention illustrated in FIG. 3, although the present invention
is not restricted to the production method described below.
[0082] In the step of laminating the coating layer onto the aluminum foil layer, the coating
composition (M), which contains a rare earth element-based oxide, 1 to 100 parts by
mass of a phosphoric acid or phosphate per 100 parts by mass of the rare earth element-based
oxide, an anionic polymer, and a cross-linking agent that causes cross-linking of
the anionic polymers, is applied onto the aluminum foil layer, and is then subjected
to drying, curing and baking to form the layer (M) 14m. In this manner, a coating
layer 14 comprised of the layer (M) 14m is laminated on top of the aluminum foil layer
13.
The steps of bonding the base material layer to the aluminum foil layer, and laminating
the sealant layer are then conducted in the same manner as the production method for
the lithium cell packing material 10 described above, thus completing production of
the lithium cell packing material 30.
[0083] The coating composition (M) preferably has a relationship that satisfies an expression
2 ≥ x'/a' between a total mass (a') (g) of the rare earth element-based oxide, and
the phosphoric acid or the phosphate, and a total mass (x') (g) of the anionic polymer
and the cross-linking agent that causes cross-linking of the anionic polymers.
Unsatisfaction of the expression 2 ≥ x'/a' necessarily means the decrease in the proportion
of the contact between the aluminum foil layer 13, and the rare earth element-based
oxide having the function for protecting the aluminum foil from corrosion and the
phosphoric acid or the phosphate, and therefore, it becomes difficult to obtain the
corrosion prevention effect for the aluminum foil layer 13. In addition, the proportion
of the anionic polymer within the layer (M) 14m increases, and consequently, it becomes
difficult to complex all of the anionic polymers with the rare earth element-based
oxide and the phosphoric acid or phosphate. Therefore, the desired functions of electrolyte
solution resistance and hydrofluoric acid resistance may not manifest satisfactorily,
resulting in deterioration in the electrolyte solution resistance and the hydrofluoric
acid resistance.
[0084] If the expression (x'/a') exceeds the above-mentioned range, then although the effects
of the present invention can still be obtained, the proportions of the anionic polymer
and the cross-linking agent tend to increase, meaning the coating composition (M)
may become more difficult to cure. The drying temperature could simply be set higher
or the curing time extended in order to ensure satisfactory curing of the coating
composition (M), but this tends to result in a fall in productivity.
Accordingly, in terms of maintaining productivity levels, while also ensuring a favorable
improvement in the electrolyte solution resistance and the hydrofluoric acid resistance,
the expression (x'/a') preferably satisfies 2 ≥ x'/a', more preferably satisfies 1.5
≥ x'/a' ≥ 0.01, and most preferably satisfies 1.0 ≥ x'/a' ≥ 0.1.
[Fourth Embodiment]
[0085] FIG. 4 is a cross-sectional view illustrating a fourth embodiment of a lithium cell
packing material 40 according to the present invention. This embodiment is described
below in detail. In FIG. 4, those structural components that are the same as those
in FIG. 1 are labeled using the same symbols, and description of these identical components
may be omitted.
<Coating Layer>
[0086] The coating layer 14 of the example shown in FIG. 4 has the multilayer structure
comprised of a cationic polymer and a cross-linking agent that causes cross-linking
of the cationic polymers in addition to the layer (M) 14m.
The layer (M) and layer (Y) are respectively the same as the layer (M) described in
the third embodiment and layer (Y) described in the second embodiment.
[0087] As described above, the anionic polymer is extremely effective material as a trap
for ion contaminants. Meanwhile, the cationic polymer is extremely effective material
as a trap for hydrofluoric acid. Furthermore, by adding a cross-linking agent to each
polymer, the water resistance can also be improved. Rather than existing in isolation,
the anionic polymer tend to exhibit more effective functionality such as electrolyte
solution resistance and hydrofluoric acid resistance when complexed with the rare
earth element-based oxide and the phosphoric acid or phosphate contained. In addition,
rather than existing in isolation, the cationic polymer also tends to exhibit more
effective functionality such as electrolyte solution resistance and hydrofluoric acid
resistance in the layer (Y) 14y when complexed with the rare earth element-based oxide
and the phosphoric acid or phosphate contained within the layer (M) 14m.
Accordingly, when the coating layer 14 is prepared as shown in FIG. 4 to be the multilayer
of the layer (M) 14 m, which contains the anionic polymer and the cross-linking agent
in addition to the rare earth element-based oxide having the function for protecting
the aluminum foil from corrosion, the phosphoric acid or phosphate, and the layer
(Y), which contains the cationic polymer and the cross-linking agent, it is possible
to obtain the lithium cell packing material that is more excellent in the electrolyte
solution resistance, the hydrofluoric acid resistance, and the water resistance while
holding the corrosion prevention effect for metal films such as an aluminum foil.
<Production Method for Packing Material for Lithium Cell>
[0088] Next is a description of a production method for the lithium cell packing material
40 of the present invention illustrated in FIG. 4, although the present invention
is not restricted to the production method described below.
[0089] In the step of laminating the coating layer onto the aluminum foil layer, the layer
(M) 14m is first formed on top of the aluminum foil layer 13 in the same manner as
the method described for the third embodiment. Subsequently, the coating composition
(Y) containing the cationic polymer and the cross-linking agent that causes cross-linking
of the cationic polymers is coated onto the layer (M) 14m, and is then subjected to
drying, curing and baking to form the layer (Y) 14y. In this manner, a coating layer
14 comprised of the layer (M) 14m and the layer (Y) 14y is laminated on top of the
aluminum foil layer 13.
The steps of bonding the base material layer to the aluminum foil layer, and laminating
the sealant layer are then conducted in the same manner as the production method for
the lithium cell packing material 10 described above, thus completing production of
the lithium cell packing material 40.
[0090] The coating composition (M) and the coating composition (Y) preferably has a relationship
that satisfies an expression 2 ≥ (x'+y')/a' among a total mass (a') (g) of the rare
earth element-based oxide, and the phosphoric acid or the phosphate, a total mass
(x') (g) of the anionic polymer and the cross-linking agent that causes cross-linking
of the anionic polymers, and a total mass (y') (g) of the cationic polymer and the
cross-linking agent that causes cross-linking of the cationic polymers.
Dissatisfaction of the expression 2 ≥ (x'+y')/a' necessarily means the decrease in
the proportion of the contact between the aluminum foil layer 13, and the rare earth
element-based oxide having the function for protecting the aluminum foil from corrosion
and the phosphoric acid or the phosphate, and therefore, it becomes difficult to obtain
the corrosion prevention effect for the aluminum foil layer 13. In addition, the proportion
of the anionic polymer within the layer (M) 14m and the proportion of the cationic
polymer within the layer (Y) 14y increase, and consequently, the proportion of the
anionic polymer that exist in isolation without being complexed with the rare earth
element-based oxide and the phosphoric acid or phosphate and the proportion of the
cationic polymer that exist in isolation without being complexed with the rare earth
element-based oxide and the phosphoric acid or phosphate contained within the layer
(M) 14m increase. Therefore, the desired functions of electrolyte solution resistance
and hydrofluoric acid resistance may not manifest satisfactorily, resulting in deterioration
in the electrolyte solution resistance and the hydrofluoric acid resistance.
[0091] If the expression {(x'+y')/a'} exceeds the above-mentioned range, then although the
effects of the present invention can still be obtained, the proportions of the anionic
polymer and the cross-linking agent and the proportions of the cationic polymer and
the cross-linking agent tend to increase, meaning the coating composition (M) and
the coating composition (Y) may become more difficult to cure. The drying temperature
could simply be set higher or the curing time extended in order to ensure satisfactory
curing of these compositions, but this tends to result in a fall in productivity.
Accordingly, in terms of maintaining productivity levels, while also ensuring a favorable
improvement in the electrolyte solution resistance and the hydrofluoric acid resistance,
the expression {(x'+y')/a'} preferably satisfies 2 ≥ (x'+y')/a', more preferably satisfies
1.5 ≥ (x'+y')/a' ≥ 0.01, and most preferably satisfies 1.0 ≥ (x'+y')/a' ≥ 0.1.
[0092] In this manner, because the lithium cell packing material of the present invention
either employs a multilayer structure comprised of the layer (A), in which the coating
layer contains a rare earth element-based oxide and the like, and the layer (X) containing
an anionic polymer; a single layer comprised of the layer (M) that contains a rare
earth element-based oxide and an anionic polymer and the like; or a multilayer structure
comprised of the layer (M), the hydrofluoric acid resistance and the water resistance
are excellent. Further, if the packing material also includes the layer (Y) containing
a cationic polymer and the like, then the electrolyte solution resistance, hydrofluoric
acid resistance and water resistance can be further enhanced.
[0093] The examples illustrated in FIG. 1 to FIG. 4 were presented as examples of the construction
of the coating layer provided in the lithium cell packing material of the present
invention, but from the viewpoint of inhibiting corrosion of the aluminum foil, the
proportion over which the rare earth element-based oxide and the phosphoric acid or
phosphate makes direct contact with the aluminum foil is preferably as large as possible.
On the other hand, from the viewpoint of ensuring effective manifestation of the electrolyte
solution resistance function, the anionic polymer and the cross-linking agent that
causes cross-linking of the anionic polymers are preferably complexed with the rare
earth element-based oxide and the phosphoric acid or phosphate. In light of these
facts, the coating layer is preferably a multilayer structure such as those illustrated
in FIG. 1 and FIG. 2, although even with the single layer structure comprised of the
layer (M) shown in FIG. 3 or the multilayer structure comprised of the layer (M) and
the layer (Y) shown in FIG. 4, the effects of the present invention can still be satisfactorily
achieved.
[0094] Furthermore, according to the present invention, a corrosion inhibiting effect for
metal foils such as aluminum foil can be obtained even with a conventional coating
method, meaning the production process for the lithium cell packing material can be
simplified without any adverse impact on the environment.
In other words, the functionality required of a lithium cell packing material can
be obtained by simply providing the coating layer 14 on the aluminum foil layer 13.
As a result, production is possible not only of the types of structures illustrated
in FIG. 1 to FIG. 4, which are produced via a dry/wet process that uses an adhesive
resin layer and either extrusion lamination or thermal lamination, but also of the
types of structures illustrated in FIG. 5 to FIG. 8, which are produced via a simpler
dry lamination process using a second adhesive layer 15a. In one example of the production
method employed for the structures illustrated in FIG. 5 to FIG. 8, a coating layer
14 described above in the first to fourth embodiments is provided on one surface of
an aluminum foil layer 13, a base material layer 11 is laminated via a first adhesive
layer 12 to the other side of the aluminum foil layer 13, and a sealant layer 16 is
then laminated to the coating layer 14 via a second adhesive layer 15a.
EEXAMPLES
[0095] Test examples of the present invention are presented below, although the present
invention is in no way limited by these examples.
[Used Materials]
[0096] The common materials used in the following test examples are listed below.
<Coating Layer 1: Layer (A) containing Rare Earth Element-Based Oxide and the Like>
[0097]
A-1: A "sodium polyphosphate-stabilized cerium oxide sol" prepared using distilled
water as the solvent and having a solid fraction concentration of 10 wt%. The cerium
oxide sol was obtained by adding 10 parts by mass of the sodium salt of the phosphoric
acid to 100 parts by mass of cerium oxide.
A-2: A "sodium polyphosphate-stabilized cerium oxide sol" prepared using distilled
water as the solvent and having a solid fraction concentration of 10 wt%. The cerium
oxide sol was obtained by adding 0.5 parts by mass of the sodium salt of the phosphoric
acid to 100 parts by mass of cerium oxide.
A-3: An "acetic acid-stabilized cerium oxide sol" prepared using distilled water as
the solvent and having a solid fraction concentration of 10 wt%. The cerium oxide
sol was obtained by adding 10 parts by mass of the sodium salt of the phosphoric acid
to 100 parts by mass of cerium oxide.
<Coating Layer 2: Layer (X) containing Anionic Polymer and the Like>
[0098]
X-1: An "ammonium polyacrylate" prepared using distilled water as the solvent and
having a solid fraction concentration of 5 wt%.
X-2: A composition composed of 90 wt% of an "ammonium polyacrylate" and 10 wt% of
an "acrylic-isopropenyloxazoline copolymer", prepared using distilled water as the
solvent and having a solid fraction concentration of 5 wt%.
<Coating Layer 3: Layer (Y) containing Cationic Polymer and the Like>
[0099]
Y-1: A composition prepared by adding 5 parts by mass of "aminopropyltrimethoxysilane"
to 100 parts by mass of the mixture of 90 wt% of a "polyallylamine" and 10 wt% of
a "1,6-hexanediol epichlorohydrin adduct" which was prepared using distilled water
as the solvent and had a solid fraction concentration of 5 wt%.
<Coating Layer 4: Layer (Y) containing Rare Earth Element-Based Oxide and Anionic
Polymer and the Like>
[0100]
M-1: A composition prepared by mixing A-1 and X-2 in which the mass a' of A-1 was
80 mg and the mass x' of X-2 was 25 mg.
<Heat-Resistant Base Material Layer>
[0101]
D-1: a biaxially oriented polyamide film (25 µm).
<Aluminum Foil Layer>
[0102]
E-1: An annealed lightweight aluminum foil No. 8079 (40 µm).
The number "8079" is an alloy number listed in JIS H 4160 (standard name: "Aluminum
and aluminum alloy foils") of the JIS standards (Japanese Industrial Standards).
<Adhesive Resin Layer and Sealant Layer>
[0103]
F-1: a multilayer polypropylene film (a cast film: 30 µm).
F-2: a maleic anhydride-modified polypropylene resin (MFR = 12 extrusion lamination
grade)
F-3: a composition prepared by blending a toluene-dispersed maleic anhydride-modified
polypropylene resin (a baked resin, solid fraction: 17 wt%) with a tolylene diisocyanate
adduct (solid fraction: 75 wt%) and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (solid
fraction: 100 wt%), using a blend ratio of 72/6/22.
[Preparation and Method of Evaluating Lithium Cell Packing Materials]
<Packing Material Preparation 1>
[0104] First, the composition used for forming each coating layer (namely, the compositions
A-1 to A-3, X-1 to X-2, Y-1, and M-1) was coated onto an aluminum foil coil (E-1)
using an appropriate microgravure coating method, and a baking treatment was then
performed in a drying unit at a temperature within a range from 150 to 250°C in accordance
with the components of that particular coating layer, thereby laminating the coating
layer onto the aluminum foil.
Subsequently, using a dry lamination method, a heat-resistant base material layer
(D-1) was provided on the opposite surface of the aluminum foil layer from the coating
layer with a polyurethane-based adhesive (A525/A52, manufactured by Mitsui Chemicals
Polyurethane, Inc.) disposed therebetween. With the resulting laminate set on the
winder portion of an extrusion lamination machine, and the sealant layer (F-1) set
as the sandwich base material, a 20 µm thick layer of the adhesive resin (F-2) was
subjected to sandwich lamination under process conditions including 290°C and 80 m/minute.
Subsequently, a sealant layer was laminated on top of the coating layer via an adhesive
resin layer. Thermocompression bonding (heat treatment) was then conducted to complete
preparation of the packing material for a lithium cell.
<Packing Material Preparation 2>
[0105] The steps up to and including the provision of the heat-resistant base material layer
(D-1) by dry lamination were performed in the same manner as the packing material
preparation 1. Subsequently, the adhesive resin (F-3) was coated onto the coating
layer using a gravure coating technique in an amount sufficient to yield a dry thickness
of 5 µm, and a baking treatment was performed. Subsequently, the sealant layer (F-1)
as subjected to thermal lamination in an in-line process, thus completing preparation
of the packing material for a lithium cell.
<Evaluations>
[0106] Each of the prepared lithium cell packing materials was cut into strip-shapes samples
having a size of 100 × 15 mm for the purposes of evaluation, and the evaluations described
below were then performed.
(Electrolyte Solution Resistance Evaluation 1: Evaluation of Organic Solvent Resistance)
[0107] An electrolyte solution was prepared by adding 1.5 M of LiPF
6 to a solution of ethylene carbonate / diethyl carbonate / dimethyl carbonate = 1/1/1,
and this electrolyte solution was then placed inside a Teflon (a registered trademark)
container having an internal capacity of 250 ml. A sample was then inserted into the
container, and the container was sealed, and then stored for 3 hours at 85°C. The
state of peeling of the sample following storage was evaluated against the criteria
listed below.
○: no delamination occurred, the laminate strength is at a level that makes peeling
difficult, or at a level that results in rupture of the sealant layer (good).
△: no delamination occurred, but the laminate strength is at a level that means peeling
is possible (at least 100 gf/15 mm, crosshead speed: 300 mm/minute) (fair).
×: layer lifting due to peeling was observed (unsatisfactory).
(Electrolyte Solution Resistance Evaluation 2: Evaluation of Hydrofluoric Acid Resistance)
[0108] A sample that had been subjected to the electrolyte solution resistance evaluation
1 was immersed in water overnight, and the state of peeling of the sample was evaluated.
The evaluation criteria were the same as those listed above for the electrolyte solution
resistance evaluation 1.
(Electrolyte Solution Resistance Evaluation 3: Evaluation of Hydrofluoric Acid Resistance)
[0109] With the exception of using the electrolyte solution of the electrolyte solution
resistance evaluation 1 to which 1,500 ppm of water had been added as the test electrolyte
solution, an evaluation was conducted in the same manner as the electrolyte solution
resistance evaluation 1. Subsequently, the sample was immersed in water overnight,
and the state of peeling of the sample was then evaluated. The evaluation criteria
were the same as those listed above for the electrolyte solution resistance evaluation
1.
(Water Resistance Evaluation)
[0110] Notches were inserted in advance in the sample to facilitate peeling, and the notched
sample was then immersed in water overnight, and the state of peeling of the sample
was then evaluated. The evaluation criteria were the same as those listed above for
the electrolyte solution resistance evaluation 1.
(Strength Evaluation)
[0111] Each of the samples obtained via the methods described above was folded so that the
sealant layer surfaces faced each other, and heat sealing was then conducted for 3
seconds under conditions including 190°C and 0.3 MPa. The sample was then cut into
strips of width 15 mm, and a universal tester (Tensilon, manufactured by Orientec
Co., Ltd.) was used to evaluate the heat seal strength and the state of rupture when
a T-type peeling measurement was conducted at a crosshead speed of 300 mm/minute.
The evaluation criteria are listed below. An evaluation result of O was taken as a
passing grade.
○: the strength was not less than 40 N/15 mm, and the rupture mode involved peeling
at a location other than the aluminum foil layer / coating layer interface or the
vicinity thereof (good).
×: either the strength was less than 40 N/15 mm, or the strength was at least 40 N/15
mm but the rupture mode involved peeling in the vicinity of the aluminum foil layer
/ coating layer interface (unsatisfactory).
(Overall Evaluation)
[0112] The evaluation results above were combined, and an overall evaluation was made based
on the following criteria.
○○: all the evaluation results were ○ (excellent).
○: of all the evaluation results, four were ○, and the remainder was △ (good). △:
of all the evaluation results, three were ○, and the remainder were △ (fair).
×: of all the evaluation results, two or fewer were ○, or at least one of the electrolyte
solution resistance evaluations was × (unsatisfactory).
[Examples 1 to 6]
[0113] Using the materials shown in Table 1, lithium cell packing materials were prepared
using the packing material preparation 1 in the case of Examples 1 to 4 and 6, or
using the packing material preparation 2 in the case of Example 5. Each of the lithium
cell packing materials was then subjected to the various evaluations described above.
The results are shown in Table 1.
[Comparative Examples 1 to 5]
[0114] Using the materials shown in Table 1, lithium cell packing materials were prepared
using the packing material preparation 1, and then subjected to the various evaluations
described above. The results are shown in Table 1.
[0115]
[Table 1]
|
|
Heat-resistant base material layer |
Aluminum foil layer |
Coating layer |
Adhesive resin layer |
Sealant layer |
Electrolyte solution resistance evaluation |
Water resistance evaluation |
Strength evaluation |
Overall evaluation |
First layer (mass *1) |
Second layer (mass *1) |
Evaluation 1 |
Evaluation 2 |
Evaluation 3 |
Example |
1 |
D-1 |
E-1 |
A-1 (80 mg/m2) |
X-2 (25 mg/m2) |
F-2 |
F-1 |
○ |
○ |
○ |
○ |
○ |
○○ |
2 |
D-1 |
E-1 |
A-1 (250mg/m2) |
X-2 (25 mg/m2) |
F-2 |
F-1 |
○ |
○ |
○ |
○ |
△ |
○ |
3 |
D-1 |
E-1 |
A-1 (80mg/m2) |
X-2 (100 mg/m2) |
F-2 |
F-1 |
○ |
○ |
△ |
○ |
○ |
○ |
4 |
D-1 |
E-1 |
A-1 (80mg/m2) |
X-2/Y-1 *2 (25 mg/m2 each) |
F-2 |
F-1 |
○ |
○ |
○ |
○ |
○ |
○○ |
5 |
D-1 |
E-1 |
A-1 (80 mg/m2) |
X-2 (25 mg/m2) |
F-3 |
F-1 |
○ |
○ |
○ |
○ |
○ |
○○ |
6 |
D-1 |
E-1 |
|
M-1 |
F-2 |
F-1 |
○ |
○ |
△ |
○ |
○ |
○ |
Compara tive Example |
1 |
D-1 |
E-1 |
A-1 (80 mg/m2) |
- |
F-2 |
F-1 |
○ |
△ |
△ |
○ |
○ |
△ |
2 |
D-1 |
E-1 |
A-2 (80 mg/m2) |
- |
F-2 |
F-1 |
- |
- |
- |
- |
- |
- |
3 |
D-1 |
E-1 |
(25 mg/m2) |
- |
F-2 |
F-1 |
○ |
× |
× |
× |
○ |
× |
4 |
D-1 |
E-1 |
X-2 (25 mg/m2) |
- |
F-2 |
F-1 |
○ |
△ |
× |
○ |
○ |
× |
5 |
D-1 |
E-1 |
A-3 (80 g/m2) |
X-2 (25 mg/m2) |
F-2 |
F-1 |
× |
× |
× |
○ |
× |
× |
* 1: mass per unit surface area of layer, *2: second layer / third layer |
[Example 7, Comparative Example 6]
[0116] Examples 1 to 6 and Comparative Examples 1 to 5 represent structures in which a lithium
cell level of performance is achieved by using a technique such as thermocompression
bonding (heat treatment) or thermal lamination, and a feature of these techniques
is the use of an adhesive resin (the acid-modified polyurethane resin). Example 7
and Comparative Example 6 describe cases in which this type of adhesive resin is replaced
with a polyurethane-based adhesive used in dry lamination.
[0117] The production method used for the packing material of Example 7 and Comparative
Example 6 is described below. First, the composition used for forming each coating
layer was coated onto an aluminum foil coil (E-1) using an appropriate microgravure
coating method. A baking treatment was then performed in a drying unit at a temperature
within a range from 150 to 250°C in accordance with the components of the coating
layer, thereby laminating the coating layer onto the aluminum foil.
Subsequently, using a dry lamination method, a heat-resistant base material layer
(D-1) was provided on the opposite surface of the aluminum foil layer from the coating
layer with a polyurethane-based adhesive (A525/A52, manufactured by Mitsui Chemicals
Polyurethane, Inc.) disposed therebetween. A dry lamination method was then used to
provide a polyurethane-based adhesive, containing a polyester polyol as the main component
and an isophorone diisocyanate isocyanurate as a curing agent, on the side of the
coating layer, using a dry coating amount of 5 g/m
2. Subsequently, a sealant layer (F-1) was laminated to the polyurethane-based adhesive.
The laminate was then aged for 5 days at 60°C, completing preparation of a lithium
cell packing material.
[0118] Using the materials shown in Table 2, tests were performed using the dry laminate
structures described above. The evaluation methods used and the evaluation criteria
are as described above.
[0119]
[Table 2]
|
Heat-resistant base material layer |
Aluminum foil layer |
Coating layer |
Adhesive layer |
Sealant layer |
Electrolyte solution resistance evaluation |
Water resistance evaluation |
Strength evaluation |
Overall evaluation |
First layer (mass *1) |
Second layer (mass *1) |
Evaluation 1 |
Evaluation 2 |
Evaluation 3 |
Example 7 |
D-1 |
E-1 |
A-1 (80 mg/m2) |
Y-1 (25 mg/m2) |
*3 |
F-1 |
○ |
△ |
△ |
○ |
○ |
△ |
Comparative Example 6 |
D-1 |
E-1 |
X-2 (25 mg/m2) |
- |
*3 |
F-1 |
○ |
× |
× |
○ |
○ |
× |
*1: mass per unit surface area of layer
*3: a polyurethane-based adhesive containing a polyester polyol as the main component,
and using an isophorone diisocyanate isocyanurate as a curing agent |
[0120] In those cases where the coating layer was a 2-layer structure comprised of the layer
(A) formed by blending a Na salt of a phosphoric acid with a rare earth element-based
oxide, and a layer (X) containing an anionic polymer and the like (Examples 1 to 3),
and the case where the coating layer was a 3-layer structure that included a layer
(Y) containing an cationic polymer and the like in addition to the layer (A) and layer
(X) (Example 4), not only was excellent organic solvent resistance achieved, but the
hydrofluoric acid resistance and water resistance were also excellent. In those cases
where the relationship (x/a) between the mass (a) of the layer (A) and the mass (x)
of the layer (X) satisfied the expression 1.0 ≥ x/a ≥ 0.1, the hydrofluoric acid resistance
was particularly favorable, even under more severe conditions. Furthermore, in those
cases where the mass of the layer (A) was 80 mg/m
2, the strength of the packing material was also favorable.
Further, even if the production method for the lithium cell packing material was altered
(Examples 5), excellent organic solvent resistance, hydrofluoric acid resistance and
water resistance similar to that obtained in Examples 1 to 4 were achieved, and the
strength was also favorable.
Furthermore, even if the coating layer was the single layer structure comprised of
the layer (M) containing a rare earth element-based oxide and an anionic polymer and
the like. (Example 6), excellent organic solvent resistance, hydrofluoric acid resistance
and water resistance were achieved, and the strength was also favorable.
Moreover, as is evident from the overall evaluation results, the lithium cell packing
materials obtained in Examples were superior to the lithium cell packing materials
obtained in Comparative Examples in terms of functional performance such as resistance
and strength.
[0121] In contrast, in the case where the coating layer was a single layer structure comprised
of the layer (A) (Comparative Example 1), although the organic solvent resistance,
water resistance, and strength were similar to those observed for Examples, the hydrofluoric
acid resistance was slightly inferior to that of Examples.
In Comparative Example 2, because the blend amount of the Na salt of the phosphoric
acid within the layer (A) was insufficient, the dispersion stabilization of the rare
earth element-based oxide was inadequate, which made application of the coating layer
impossible, meaning a lithium cell packing material could not be obtained.
In those cases where the coating layer was a single layer structure comprised of the
layer (X) (Comparative Examples 3 and 4), although the organic solvent resistance
and strength were similar to those observed for Examples, the hydrofluoric acid resistance
was markedly inferior to that of Examples. In particular, in the case where the coating
layer contained no cross-linking agent (Comparative Example 3), the water resistance
was also unsatisfactory.
In Comparative Example 5, acetic acid was used as the dispersion stabilizer, and therefore
the organic solvent resistance and hydrofluoric acid resistance were unsatisfactory.
Furthermore, the strength was also weaker than that observed for Examples.
[0122] Furthermore, these structures confirmed that excellent performance could be achieved
by using thermocompression bonding (heat treatment) and thermal lamination, but satisfactory
performance as a lithium cell packing material was also able to be maintained using
a dry laminate structure. Accordingly, in the present invention, it was confirmed
that by interposing the coating layer described above, favorable performance as a
lithium cell packing material could be achieved, regardless of the production method.
INDUSTRIAL APPLICABILITY
[0123] According to the present invention, a packing material for a lithium cell that exhibits
excellent electrolyte solution resistance, hydrofluoric acid resistance and water
resistance, as well as favorable strength properties can be obtained without performing
conventional chemical conversion treatments such as chromate treatments. Accordingly,
the present invention is very useful industrially.